After Going beating the game. and saving continue from that file and start a mission and when you can select your aircraft, hit the Square button to access a 2nd hanger which will Contain the Vic Viper and MX5000.
Unlock Ellen Mcnlchol
To Unlock Ellen (Ken's Ex). Go through the game and focus on Albert with ken. and shoot him down every time he is on the map.
Eventually you will see a cutscene of him finding Ellens past. Later on after that. there will be another cutscene of her landing at the base with a note from Albert.
NOTE - Ellen is only playable during the last few missions(Preferably The Space Ones)